Compensating piston



D. MILLER Aug. 26, 1930.

COMPE'NSAT I NG PI STON Filed Nov. 18, 1929 2 Sheets-Sheet 1 Fig.1 7

COMPENSATING PISTON Filed Nov, 18, 1929 2 Sheets-sheet 2 Fig. 7 Fig, 6

gwoento a Patented Aug. 26, 1930 UNITED STATES DORE MILLER, OF DETROIT, MICHIGAN comrnu'sn'rme rrs'rou Application filed November 18, 1929. Serial No. 407,852.

This invention relates to pistons of the flexible skirt type, but more to pistons of alloy containing aluminum, where it is necessary to compensate for the relatively great expan- 5 sion and contraction of the metal.

An important obj ect'is to produce a piston of the flexible skirt type, which is so constructed as to compensate for the expansion of the skirt in accordance with the heat con- 1 ditions, thereby to limit the pressure of the skirt on the cylinder walls.

Other objects and advantages will appear as the description proceeds, and for purposes of illustration, and not of limitation, the in- 15 vention is. shown on the accompanying drawings, in which:

Fig. 1 is a side elevation of the rough piston casting partly in section showing the piston after being taken from the mold;

Fig. 2 is a side elevation of the finished piston;

Fig. 3 is a longitudinal sectional elevation on the line 3-3 of Fig. 2; r

Fig. 4 is a longitudinal sectional elevation 5 on the line 4-4 of Fig. 3;

Fig. 5 is a sectional elevation on the line 5-5 of Fig. 6;

Fig. 6 is a transverse section on the line 66 of Fig. 2;

Fig. 7 is an end view of the rough piston casting" shown in Fig. 1;

Fig. 8 is a longitudinal section on the line 8-8 of Fig. 6;

Fig. 9 is a diagrammatic view showing in exaggerated form the position of the inner skirt relative to the outer skirt when pressure is exerted in the direction ofthe arrows; and

Fig. 10 is a diagrammatic view showing the relative-position of the parts where force is exerted in the direction of the arrows.

Referring to the drawings, the piston comprises a circular skirt 1 and head 2, the cirskirt 1, and through these openings extend- 5 piston pin bosses 4. The bosses 4 are eon save weight in metal.

cular wall of the latter being sufficiently nected by an arm 4 integrally with the fiat and circular side wall portions of the head 2. For afiording additional strength to the fiat portion of the head 2, and joining the arms 4, the ribs 4 integral with the head.

As particularly shown in Figs. 3 and 5, the integral surfaces of the bosses 4 and arms 4 are substantially unbroken in a longitudinal direction providing a plane at substantially right angles to the'internal surface of the flat portion of the head 2. This feature is of importance in the casting of the piston as it eliminates under-cuts which militate against the use of a unitary core.

Within the outer skirt 1 is an inner skirt 8, which is in substantially concentric relation to the outer skirt and is cast integral with the head 2 and bosses 4, as will be hereinafter described. The outer skirt 1 and inner skirt 8 are severed from the head 2 providing a space 5 therebetween so that the outer skirt 1 is spaced from the head 2, but is connected thereto by the inner skirt 8, bosses 4 and arms 4. As particularly shown in Fig. 5, the aggregate thickness of the outer skirt 1, inner skirt 8, and space therebetween, is equal to the thickness of the circular wall ofthe head 2. I

'In the finished form of the piston the inner. skirt 8 rovides two separate portions, each portion eing integral with a boss 4 and with the outer skirt 1 at points remote from the respective boss. The inner skirt 8 could be a complete circle with one or more points of attachment to the outer skirt 1, but the shown division of the inner skirt has been made-to give the outer skirt required support and to The length of the inner skirt is governed by the desired strength, and the sections of the inner skirt after machining may be termed struts or supports.

The outer skirt 1 is divided into two separate portions, and in this instance diagonal slits 7 in the region of the bosses 4 are formed, and this division may be made either under the bosses 4, or between the inner skirt or strut portions 8.

In use it will be manifest that the head 2 does not contact with the walls of the cylintier, but the usual rings in the grooves 6 form the contact between the head and cylinder Wall. By virtue of the above construction the skirt maintains substantially uniform contact with the cylinder walls under all conditions. Although this invention is not confined to the use of an aluminum alloy piston, it is of particular use when the piston contains aluminum which has considerable propensity to expansion when subjected to heat. When heated the outer skirt 1 will, of course, expand circumferentially as the cylinder walls limit its expansion in a radial direction.

In order to compensate for the expansion of the skirt 1, thereby to limit the pressure on the cylinder walls, the inner skirt portions or strut members Sperform their important function. WVhen these members 8 are heated, due to their curvature they expand outwardly toward the outer skirt 1, and in this manner limit expansion of the outer skirt 1. It is, therefore, apparent that the maximum pressure on the cylinder walls caused by the expansion of the piston is limited by the flexibility of the inner and outer skirts, and such flexibility is governed by'the thickness of the walls, which is chosen according to commercial requirements. The outward bowing of the inner skirts or strut members 8 is clearly demonstrated in exaggerated form in Fig. 10, in which arrows indicate pressure directed on diametrically opposed points. In order further to indicate the flexibility of the piston, Fig. 9 indicates in exaggerated form the relation of the parts when pressure is exerted thereagainst at diametrically opposed points indicated by the arrows in connection therewith in the region of the bosses 4.

It will be seen that I have provided a construction which satisfies the objects enumerated above, and one which constitutes a valuable advance in the art. While I have shown the invention in a certain physical embodiment, it is to be understood that modifications of the structure shown may be made by those skilled in this art without departing from my invention, as expressed in the following claims.

What I claim as new and desire to secure by Letters Patent is:

1. An alloy piston of the type comprising a head, integral with'and depending from said head, a divided outer skirt free from said head, inner skirts separate from said head integral with said bosses, said inner skirts being spaced inwardly from said outer skirt and substantially concentric therewith, and an integral connection between'said inner skirts and said outer skirt in the region disposed at substantially 90 to a line taken centrally throu 11 said piston pin bosses.

2. in alloy piston of the compensating type comprising a head, a pair of oppositely arranged piston pin bosses integral with said compensating piston pin bosses head, an outer skirt entirely free from said head, inner skirts separate from said head and concentric with said outer skirt, integral 

